There are three new Angle Dimension components in Rhino 8. They are:

Angle Dimension from Lines

Angle Dimension from Points

Angle Dimensions from an Arc

Hopefully, the Angle Dimension from Lines and Points are pretty straightforward. I should note that the direction of the lines is what causes a dimension arc to be drawn on the “outside” or the “inside” of the angle measurement. So, if you’re getting inconsistent results, try flipping the curve direction on one or both of the lines you’re using for the angle dimension.

Now, the component you had a question about (Angle Dimension from an Arc) did have a bug in it. I have fixed this and it should be available in the next release. But theoretically, you just have to provide an arc and an offset and it will generate a new Angular Dimension based on those values. I’ve provided a screenshot and the definition so you can see for yourself. Note, Angle Dimension from Arc component wont work correctly until the next WIP is released next week.